The Data-Over-Cable Service Interface Specification (DOCSIS) was established by cable television network operators to facilitate transporting data traffic, primarily Internet traffic, over existing community antenna television (CATV) networks. In addition to transporting data traffic, as well as television content signals over a CATV network, multiple services operators (MSO) also use CATV network infrastructure for carrying voice, video on demand (VoD) and video conferencing traffic signals, among other types.
In addition to the MSO providing services over a hybrid fiber-coax (HFC) network, services may also be provided through a radio frequency over glass (RFoG) network, which generally includes a topology that can allow for an MSO to provide for a fiber architecture from the headend to a field node at a user's location (the field node may also be referred to as an optical network unit (ONU)). When more than one ONU in an RFoG network transmits upstream at any one time, transmission interference issues such as, for example, optical beat interference (OBI) can arise.
OBI can occur when one or more RFoG ONUs transmit contemporaneously to the same receiver, and contain wavelengths which are sufficiently close to each other. Moreover, OBI can be the result of the heterodyning of the two (or more) closely spaced wavelengths present on the same detector. Heterodyning results in the mixing products of the optical frequencies of two or more lasers appearing as wideband noise in the RF domain. The resulting noise can impact the signal integrity, thereby adversely affecting upstream transmissions. However, various systems and methods can be implemented in a cable modem termination system (CMTS) to aid in reducing transmission interference in an RFoG network. Such systems and methods seek to accomplish reducing OBI while utilizing state information readily available to the CMTS thereby reducing unnecessary complexity to existing systems.
Like reference numbers and designations in the various drawings indicate like elements.